Highly loaded low pressure mercury vapor discharge lamp



Dec. 8, 1964 H. DzlERGwA ETAL 3,160,778l

HIGHLY LOADED Low PRESSURE MERCURY VAPOR DISCHARGE LAMP Filed March 28, 1962 v vvvv D ga/ AMMAMA ,0

07, n, n, 65% cd) \70z cd Cd lrwerwrbo: Her'befft Dzievwa Lofiha- B Sch b fw Their AflfL-Qrweg United tetes i 3,160,778 Patented Dec. 8, 1964 4 Claims. (Cl.l :n3-179) This invention relates to highly loaded low pressure mercury vapor discharge lamps, more particularly to fluorescent lamps subject to higher electrical orthermal loads than customary hitherto. Such lamps contain, besides a starting gas such as argon at a few millimeters pressure to facilitate starting of the discharge in the mercury vapor, special additions of amalgams or amalgam-forming metals or alloys. ,Y lt is well known that in fluorescent lamps wherein the luminescent layer applied to the inner wall of the envelope is excited to light emission by the resonance radiation of mercury vapor, there is an optimum value of mercury vapor pressure for most eflicient operation, such value falling in the range of 5 to 10 microns corresponding to the vapor pressure of mercury between 38 C. and 45 C. In the case of higher electrical or thermal loading of the lamp, the bulb wall temperature rises with attendant'increase` in mercury vapor pressure beyond the optimum, thus resulting in a reduced amount of efficiency of resonance radiation. The addition of an amalgam within the envelope counteracts the effect of the rise in bulb wall temperature resulting from increased electrical or thermal loading in that it reduces the mercury vapor' pressure,

, thereby allowing the luminous eiiiciency to increase with resultant improvement in eiliciency of these lamps.

The extent to which the mercury vapor pressure is decreased depends on the composition of the amalgam. As disclosed in U.S. Patent 3,007,071-Lompe et al., the amalgam-forming metals may consist of cadmium, thallium, indium, gallium, etc. In order to insure that these metals decrease the vapor pressure, the requirement must ,i be met that they be located at denite places within the copending application Serial No. 31,782, tiled May 31,`

1960, of Herbert Dziergwa et al., entitled Fluorescent Lamp With Low Melting Amalgam Filling, or in the division thereof, Serial No. 299,134, filed .Tune 10, 1963, entitled Fluorescent Lamp and Method of and Apparatus for Manufacturing Such Lamps, and assigned to the same assignee as the present invention. In spite of the aforesaid measures, good adhesion of the amalgam to the envelope wall represents a critical point in the technology ofV amalgam lamps, particularly where the lamps are subject to high mechanical stresses such as shocks and bumps as frequently occur where the lamps are used for vehicular or train illumination, or when the lamps are improperly mounted.

The general object of the present invention is to pro ide an improved high output, highly Vloaded low .pressure mercury vapor discharge lamp.

A more specific object is to provide improved adhesion of the amalgam or amalgam-forming alloy to the envelope wall.

FIG. 1 of the drawing is a triangular coordinate diagram showing the composition range of a preferred :amalgam in accordance with the invention.

FIG. 2 shows a fluorescent lamp embodying the invention.

The lforegoing requirements and objects of the present invention, and others which will become apparent as the description proceeds, are achieved byV the use of an amalgam characterized as a three-component system so composed that its lower melting point, given by the solidus Curve, is higher than C. and further characterized by v fast adhesion to the place of application even despite shocks to the lamp coming near to the breaking strain of the glass. Such three-component system amalgams achieve good reliable adhesion because at the temperatures generally below 90 C. which they attain in highly loaded lamps, they are plastically deformable While remaining in a solid state or aggregation, that is the amalgam does not reach its lower melting point given by the solidus curve.

Amalgams characterized by three component systems in accordance with the invention show to a surprising extent the properties of an excellent adhesive. In this respect, they are in decided contrast to the non-metallic organic or inorganic adhesives used in known vacuum tight seals of glass to other materials such as metals and which tend to increase the vapor pressure in unsuitable manner at the operating temperatures prevailing in the lamp and thereby deleteriously iniluence the voltage gradient and the efiiciency of the lamp. They also contrast with the known metallic adhesives used for vacuum tight connections whics have"neither the adhesion of the amalgams herein nor their vapor pressure reducing effect. The threecomponent systems which are particularly suitable in accordance with the invention are Hg-Sn--Cd, Hg-Bi-Cd and especially the indium-containing Ythreecomponent systems Hg-In-TL Hg-ln-Zn and Hg-In-Cd, all of which have quite low vapor pressures and tend to decrease the mercury vapor pressure.

The strong vapor pressure decreasing efect of the amalgams in accordance with the invention and the fact that they do not require any additional adhesive to secure them in place means that small quantities of amalgam are sufficient for `the purpose. As a result, the strain on the envelope wall due to the weight ofthe amalgam body is slight and the risk of loosening from the place of attachment is that much less.

Another noteworthy advantage of amalgams according to the invention resides in the fact that they consist of only a few components. Alloys or alloy mixtures consisting of many components have a tendency to develop several chemical phases which may coexist simultaneously. The behavior of these different phases is diflicult to determine accurately and phase changes may occur slowly during lamp oper-ation with a resultant deleterious effect on adhesion and vapor pressure decreasing effect.

A preferred three-component system in accordance with the invention which meets to an unusual degree the desiderata in respect of solidus temperature, good adhe- V sion and vapor pressure reducing effect is an indium-cadmium amalgam the composition of which lies either in region I or in contiguous region ll in the system mercurycadmium-indium wherein the regions are deiined as follows.

Region l-The following requirements must be met simultaneously:

(l) The percentage (Cd) of cadmium in atoms per- (3) The percentage (Cd) of cadmium in atoms percent, for the selected percentage of mercury, must be not lower than would tit the equation:

Region II-The following requirement must be met simultaneously:

(l) The percentage (Hg) of mercury in atoms percent must lie between 0.5% and 15%. (2) The percentage (Cd) of cadmium in atoms percent, for the selected percentage of mercury, must be lower than would lit the equation:

(3) The percentage (In) of indium in atoms percent follows from the requirement:

Particularly favorable results have been obtained with ndium-cadmium-amalgams the composition of which lie in the regions I or II' in the system mercurycadmium indium, which regions are more narrowly deiined as follows.

Region I-Meeting the following requirements:

(1) Percentage (Cd) of cadmium in atoms percent not higher than 65% (2) Percentage (Hg) of mercury in atoms percent between 0.5% and 65%.

(3) Percentage (Cd) of cadmium for the selected percentage of mercury not lower than would fit the equation:

(Hg) +3(Cd)=170% Region II'-Meeting the following requirements:

(l) Percentage (Hg) of mercury in atoms percent lying between 0.5% and 10%. (2) Percentage (Cd) of cadmium in atoms percent, for the selected percentage of mercury, lower than would t the equation:

(Hg) +3(Cd)=170% (3) Percentage (In) of indium in atoms percent following from the requirement:

(HgH-(Cd) -l-(In)=100% For very highly loaded lamps, a more favorable region is characterized by a mercury percentage falling between 20 and 45 atoms percent.

The entire composition range of indium-cadmium amalgams may be represented on a triangular coordinate diagram as shown in the drawing wherein the three intersecting coordinates represent the cadmium, indium, or mercury atom percentages of the alloy. For any point within the diagram, the atom percentages of the three components add up to 100%. The desirable region in accordance with the invention consists of the two partial contiguous regions I and II. Region I (or preferred region I) is bounded by the straight lines corresponding to 70 atom percent cadmium (or preferably 65 atom percent), 0.5 atom percent mercury, atom percent indium, and by the straight line A1A2 (or A1A2 for the preferred region). The line A1A2 (or A1A2') is given by the relationship (Hg)-}-3(Cd)=l50% (or 170% for the preferred region). The region Il (or preferred region II) is bounded by the straight lines corresponding to 0.5 atom percent mercury, 15 atom percent mercury (or preferably atom percent), 0 atom percent cadmium, and by the straight line A1A2 (or A1A2 for the preferred region) as given above. The outer boundaries of regions I and II within the diagram are lined with hatching for easier recognition.

For high output highly loaded lamps, a superior preferred region lies in region I between the straight lines A1A2' and 65 atompercent cadmium and is characterized by having a mercury percentage between 45 and 20 atoms percent. This region is cross-hatchedV in the diagram.

Indium-cadmium amalgams having such a composition decrease the mercury vapor pressure to an extent corresponding to a temperature drop of about 20 to 45 C. This is the extent to which the wall temperature would have to be decreased for optimum mercury vapor pressure in a high output highly loaded lamp containing only mercury, that is without amalgam addition.

The invention results in lamps which are electrically and thermally highly loadable and wherein the amalgam body will remain attached to the lamp envelope up to the breaking limit of the glass. A typical lamp embodying the invention is illustrated in FIG. 2 and consists of a generally conventional fluorescent lamp having an elongated tubular vitreous envelope 1. A section of the envelope wall has been cut away at 2 to reveal a compact amalgam forming body 3 adhering to the wall, such body consisting of a mercury-cadmium-indium alloy as defined herein.

The specific preferred embodiments of the invention which have been described herein are intended by way of illustrative examples, and the scope of the invention is to be determined by the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A highly loaded low pressure mercury vapor discharge lamp comprising an elongated vitreous envelope containing mercury vapor and an amalgam adherent to the envelope wall and consisting of a mercury-cadmiumindium alloy whereof the composition resides in one of two regions I and II defined as follows wherein the percentages relate the atom specified to total atoms:

Region I- (1) Percentage (Cd) of cadmium not more than (2) Percentage (Hg) of mercury between 0.5%

and 75 (3) Percentage (Cd) of cadmium for the selected percentage of mercury not less than given by:

(Hg) +3 (Cd) :150%

and Region II- (1) Percentage (Hg) of mercury between 0.5%

and 15%, (2) Percentage (Cd) of cadmium for .the selected percentage of mercury less than given by:

(HgH-S (Cd) (3) Percentage (In) of indium given by:

(Hg)+(Cd)-le(r1)=100% 2. A highly loaded low pressure mercury vapor discharge lamp comprising an elongated vitreous envelope containing mercury vapor and an amalgam body attached to fthe envelope wall at a place not subject to excessively high temperature for reducing .the mercury vapor pressure, said amalgam body consisting of a mercurycadmium-indium alloy whereof the composition resides in one of two regions I andv II defined as follows wherein the percentages relate the atom specified to total atoms:

Region I- (1) Percentage (Cd) of cadmium not more than (2) Percentage (Hg) of mercury between 0.5%

and 75%,

(3) Percentage (Cd) of cadmium for the selected percentage of mercury not less than given by:

and Region II- (1) Percentage (Hg) of mercury between 0.5% and 15%, (2) Percentage (Cd) of cadmium for the selected percentage of mercury less than given by:

(Hg) +3 (Cd) :150%

M Tuur (3) Percentage (In) of indium given by:

(Hg) -I- (Cd) (In) 100% 3. A highlyloaded low pressure mercury vapor discharge lamp comprising anV elongated vitreous envelope containing mercury vapor and an amalgam body attached to :the envelope Wall at a place not subject to excessively high temperature for reducing the mercury vapor pressure, said amalgam body consisting 0f a mercury-v cadmium-indium alloy whereof the composition resides 10 in one of two regions I and 1I deiined as follows wherein the percentages relate the atom specified to total atoms:

Region I- (1) Percentage (Cd) of cadmium not more than 65%, i (2) Percentage (Hg) of mercury between 0.5%

and 65%, (3) Percentage (Cd) of cadmium for the selected percentage of mercury not less than given by: v

(Hg) |3 (Cd) :170%

and Region 11'- 6 (1) Percentage (Hg) of mercury between 0.5%

and 10%, t (2) Percentage (Cd) of cadmium for the selected percentage of mercury less than given by: 5 (Hg)+3(cd):170%

(3) Percentage (In) of indium given by:

(Hg)l-(Cd)|(f1)=109% 4. A highly loaded, high output mercury vapor discharge lamp as defined in claim 3 characterized by a composition in region I' thereof` wherein the percentage of mercury lies between 20 and 45 atoms percent.

References Cited in the flle of this patent 

1. A HIGHLY LOADED LOW PRESSURE MERCURY VAPOR DISCHARGE LAMP COMPRISING AN ELONGATED VITREOUS ENVELOPE CONTAINING MERCURY VAPOR AND AN AMALGAM ADHERENT TO THE ENVELOPE WALL AND CONSISTING OF A MERCURY-CADMIUMINDIUM ALLOY WHEREOF THE COMPOSITION RESIDES IN ONE OF TWO REGIONS I AND II DEFINED AS FOLLOWS WHEREIN THE PERCENTAGES RELATE THE ATOM SPECCIFIED TO TOTAL ATOMS: REGION I(1) PERCENTAGE (CD) OF CADMIUM NOT MORE THAN 70%, (2) PERCENTAGE (HG) OF MERCURY BETWEEN 0.5% AND 75%, (3) PERCENTAGE (CD) OF CADMIUM FOR THE SELECTED PERCENTAGE OF MERCURY NOT LESS THAN GIVEN BY: 